// This file is part of Eigen, a lightweight C++ template library
// for linear algebra.
//
// Copyright (C) 2017 Gael Guennebaud <gael.guennebaud@inria.fr>
//
// This Source Code Form is subject to the terms of the Mozilla
// Public License v. 2.0. If a copy of the MPL was not distributed
// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.

#ifndef EIGEN_INDEXED_VIEW_H
#define EIGEN_INDEXED_VIEW_H

namespace Eigen {

namespace internal {

    template <typename XprType, typename RowIndices, typename ColIndices> struct traits<IndexedView<XprType, RowIndices, ColIndices>> : traits<XprType>
    {
        enum
        {
            RowsAtCompileTime = int(array_size<RowIndices>::value),
            ColsAtCompileTime = int(array_size<ColIndices>::value),
            MaxRowsAtCompileTime = RowsAtCompileTime != Dynamic ? int(RowsAtCompileTime) : Dynamic,
            MaxColsAtCompileTime = ColsAtCompileTime != Dynamic ? int(ColsAtCompileTime) : Dynamic,

            XprTypeIsRowMajor = (int(traits<XprType>::Flags) & RowMajorBit) != 0,
            IsRowMajor =
                (MaxRowsAtCompileTime == 1 && MaxColsAtCompileTime != 1) ? 1 : (MaxColsAtCompileTime == 1 && MaxRowsAtCompileTime != 1) ? 0 : XprTypeIsRowMajor,

            RowIncr = int(get_compile_time_incr<RowIndices>::value),
            ColIncr = int(get_compile_time_incr<ColIndices>::value),
            InnerIncr = IsRowMajor ? ColIncr : RowIncr,
            OuterIncr = IsRowMajor ? RowIncr : ColIncr,

            HasSameStorageOrderAsXprType = (IsRowMajor == XprTypeIsRowMajor),
            XprInnerStride = HasSameStorageOrderAsXprType ? int(inner_stride_at_compile_time<XprType>::ret) : int(outer_stride_at_compile_time<XprType>::ret),
            XprOuterstride = HasSameStorageOrderAsXprType ? int(outer_stride_at_compile_time<XprType>::ret) : int(inner_stride_at_compile_time<XprType>::ret),

            InnerSize = XprTypeIsRowMajor ? ColsAtCompileTime : RowsAtCompileTime,
            IsBlockAlike = InnerIncr == 1 && OuterIncr == 1,
            IsInnerPannel =
                HasSameStorageOrderAsXprType && is_same<AllRange<InnerSize>, typename conditional<XprTypeIsRowMajor, ColIndices, RowIndices>::type>::value,

            InnerStrideAtCompileTime = InnerIncr < 0 || InnerIncr == DynamicIndex || XprInnerStride == Dynamic ? Dynamic : XprInnerStride * InnerIncr,
            OuterStrideAtCompileTime = OuterIncr < 0 || OuterIncr == DynamicIndex || XprOuterstride == Dynamic ? Dynamic : XprOuterstride * OuterIncr,

            ReturnAsScalar = is_same<RowIndices, SingleRange>::value && is_same<ColIndices, SingleRange>::value,
            ReturnAsBlock = (!ReturnAsScalar) && IsBlockAlike,
            ReturnAsIndexedView = (!ReturnAsScalar) && (!ReturnAsBlock),

            // FIXME we deal with compile-time strides if and only if we have DirectAccessBit flag,
            // but this is too strict regarding negative strides...
            DirectAccessMask = (int(InnerIncr) != UndefinedIncr && int(OuterIncr) != UndefinedIncr && InnerIncr >= 0 && OuterIncr >= 0) ? DirectAccessBit : 0,
            FlagsRowMajorBit = IsRowMajor ? RowMajorBit : 0,
            FlagsLvalueBit = is_lvalue<XprType>::value ? LvalueBit : 0,
            FlagsLinearAccessBit = (RowsAtCompileTime == 1 || ColsAtCompileTime == 1) ? LinearAccessBit : 0,
            Flags = (traits<XprType>::Flags & (HereditaryBits | DirectAccessMask)) | FlagsLvalueBit | FlagsRowMajorBit | FlagsLinearAccessBit
        };

        typedef Block<XprType, RowsAtCompileTime, ColsAtCompileTime, IsInnerPannel> BlockType;
    };

}  // namespace internal

template <typename XprType, typename RowIndices, typename ColIndices, typename StorageKind> class IndexedViewImpl;

/** \class IndexedView
  * \ingroup Core_Module
  *
  * \brief Expression of a non-sequential sub-matrix defined by arbitrary sequences of row and column indices
  *
  * \tparam XprType the type of the expression in which we are taking the intersections of sub-rows and sub-columns
  * \tparam RowIndices the type of the object defining the sequence of row indices
  * \tparam ColIndices the type of the object defining the sequence of column indices
  *
  * This class represents an expression of a sub-matrix (or sub-vector) defined as the intersection
  * of sub-sets of rows and columns, that are themself defined by generic sequences of row indices \f$ \{r_0,r_1,..r_{m-1}\} \f$
  * and column indices \f$ \{c_0,c_1,..c_{n-1} \}\f$. Let \f$ A \f$  be the nested matrix, then the resulting matrix \f$ B \f$ has \c m
  * rows and \c n columns, and its entries are given by: \f$ B(i,j) = A(r_i,c_j) \f$.
  *
  * The \c RowIndices and \c ColIndices types must be compatible with the following API:
  * \code
  * <integral type> operator[](Index) const;
  * Index size() const;
  * \endcode
  *
  * Typical supported types thus include:
  *  - std::vector<int>
  *  - std::valarray<int>
  *  - std::array<int>
  *  - Plain C arrays: int[N]
  *  - Eigen::ArrayXi
  *  - decltype(ArrayXi::LinSpaced(...))
  *  - Any view/expressions of the previous types
  *  - Eigen::ArithmeticSequence
  *  - Eigen::internal::AllRange      (helper for Eigen::all)
  *  - Eigen::internal::SingleRange  (helper for single index)
  *  - etc.
  *
  * In typical usages of %Eigen, this class should never be used directly. It is the return type of
  * DenseBase::operator()(const RowIndices&, const ColIndices&).
  *
  * \sa class Block
  */
template <typename XprType, typename RowIndices, typename ColIndices>
class IndexedView : public IndexedViewImpl<XprType, RowIndices, ColIndices, typename internal::traits<XprType>::StorageKind>
{
public:
    typedef typename IndexedViewImpl<XprType, RowIndices, ColIndices, typename internal::traits<XprType>::StorageKind>::Base Base;
    EIGEN_GENERIC_PUBLIC_INTERFACE(IndexedView)
    EIGEN_INHERIT_ASSIGNMENT_OPERATORS(IndexedView)

    typedef typename internal::ref_selector<XprType>::non_const_type MatrixTypeNested;
    typedef typename internal::remove_all<XprType>::type NestedExpression;

    template <typename T0, typename T1>
    IndexedView(XprType& xpr, const T0& rowIndices, const T1& colIndices) : m_xpr(xpr), m_rowIndices(rowIndices), m_colIndices(colIndices)
    {
    }

    /** \returns number of rows */
    Index rows() const { return internal::size(m_rowIndices); }

    /** \returns number of columns */
    Index cols() const { return internal::size(m_colIndices); }

    /** \returns the nested expression */
    const typename internal::remove_all<XprType>::type& nestedExpression() const { return m_xpr; }

    /** \returns the nested expression */
    typename internal::remove_reference<XprType>::type& nestedExpression() { return m_xpr; }

    /** \returns a const reference to the object storing/generating the row indices */
    const RowIndices& rowIndices() const { return m_rowIndices; }

    /** \returns a const reference to the object storing/generating the column indices */
    const ColIndices& colIndices() const { return m_colIndices; }

protected:
    MatrixTypeNested m_xpr;
    RowIndices m_rowIndices;
    ColIndices m_colIndices;
};

// Generic API dispatcher
template <typename XprType, typename RowIndices, typename ColIndices, typename StorageKind>
class IndexedViewImpl : public internal::generic_xpr_base<IndexedView<XprType, RowIndices, ColIndices>>::type
{
public:
    typedef typename internal::generic_xpr_base<IndexedView<XprType, RowIndices, ColIndices>>::type Base;
};

namespace internal {

    template <typename ArgType, typename RowIndices, typename ColIndices>
    struct unary_evaluator<IndexedView<ArgType, RowIndices, ColIndices>, IndexBased> : evaluator_base<IndexedView<ArgType, RowIndices, ColIndices>>
    {
        typedef IndexedView<ArgType, RowIndices, ColIndices> XprType;

        enum
        {
            CoeffReadCost = evaluator<ArgType>::CoeffReadCost /* TODO + cost of row/col index */,

            FlagsLinearAccessBit = (traits<XprType>::RowsAtCompileTime == 1 || traits<XprType>::ColsAtCompileTime == 1) ? LinearAccessBit : 0,

            FlagsRowMajorBit = traits<XprType>::FlagsRowMajorBit,

            Flags =
                (evaluator<ArgType>::Flags & (HereditaryBits & ~RowMajorBit /*| LinearAccessBit | DirectAccessBit*/)) | FlagsLinearAccessBit | FlagsRowMajorBit,

            Alignment = 0
        };

        EIGEN_DEVICE_FUNC explicit unary_evaluator(const XprType& xpr) : m_argImpl(xpr.nestedExpression()), m_xpr(xpr)
        {
            EIGEN_INTERNAL_CHECK_COST_VALUE(CoeffReadCost);
        }

        typedef typename XprType::Scalar Scalar;
        typedef typename XprType::CoeffReturnType CoeffReturnType;

        EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE CoeffReturnType coeff(Index row, Index col) const
        {
            return m_argImpl.coeff(m_xpr.rowIndices()[row], m_xpr.colIndices()[col]);
        }

        EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE Scalar& coeffRef(Index row, Index col)
        {
            return m_argImpl.coeffRef(m_xpr.rowIndices()[row], m_xpr.colIndices()[col]);
        }

        EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE Scalar& coeffRef(Index index)
        {
            EIGEN_STATIC_ASSERT_LVALUE(XprType)
            Index row = XprType::RowsAtCompileTime == 1 ? 0 : index;
            Index col = XprType::RowsAtCompileTime == 1 ? index : 0;
            return m_argImpl.coeffRef(m_xpr.rowIndices()[row], m_xpr.colIndices()[col]);
        }

        EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE const Scalar& coeffRef(Index index) const
        {
            Index row = XprType::RowsAtCompileTime == 1 ? 0 : index;
            Index col = XprType::RowsAtCompileTime == 1 ? index : 0;
            return m_argImpl.coeffRef(m_xpr.rowIndices()[row], m_xpr.colIndices()[col]);
        }

        EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE const CoeffReturnType coeff(Index index) const
        {
            Index row = XprType::RowsAtCompileTime == 1 ? 0 : index;
            Index col = XprType::RowsAtCompileTime == 1 ? index : 0;
            return m_argImpl.coeff(m_xpr.rowIndices()[row], m_xpr.colIndices()[col]);
        }

    protected:
        evaluator<ArgType> m_argImpl;
        const XprType& m_xpr;
    };

}  // end namespace internal

}  // end namespace Eigen

#endif  // EIGEN_INDEXED_VIEW_H
